import 'dart:math';

const double xOrigin = 0;
const double yOrigin = 0;

class Point {
  double x = 0;
  double y = 0;

  Point(this.x, this.y);

  double distanceTo(Point other) {
    var dx = x - other.x;
    var dy = y - other.y;
    return sqrt(dx * dx + dy * dy);
  }
}

class Vector extends Object {
  final int x, y;

  Vector(this.x, this.y);

  Vector operator +(Vector v) => Vector(x + v.x, y + v.y);

  Vector operator -(Vector v) => Vector(x - v.x, y - v.y);

  bool operator ==(Object v) => hashCode == v.hashCode;

// Operator == and hashCode not shown.
// ···
}

class Rectangle {
  double left, top, width, height;

  Rectangle(this.left, this.top, this.width, this.height);

  // Define two calculated properties: right and bottom.
  double get right => left + width;

  set right(double value) => left = value - width;

  double get bottom => top + height;

  set bottom(double value) => top = value - height;
}

void rectangleTest() {
  var rect = Rectangle(3, 4, 20, 15);
  assert(rect.left == 3);
  rect.right = 12;
  assert(rect.left == -8);
}

void main() {
  rectangleTest();
}
